boards: intel_adsp: prefix "ADSP Reset" message with "invalid slot 0"

Unlike logtool.py, adsplog.py is not shielded from corrupted log data.
Lenghten the error message a bit and be more transparent about the
"invalid slot 0 => ADSP reset" assumption because it is usually but not
always true.

Signed-off-by: Marc Herbert <marc.herbert@intel.com>

boards/xtensa/intel_adsp_cavs15/tools/adsplog.py

@@ -111,7 +111,7 @@ def read_hist(start_slot):
     # be a hardware bug).
     if start_slot == 0 and id0 < 0:
         if not reset_logged:
-            sys.stdout.write("===\n=== [ADSP Device Reset?]\n===\n")
+            sys.stdout.write("===\n=== [Invalid slot 0; ADSP Device Reset?]\n===\n")
             sys.stdout.flush()
         reset_logged = True
         time.sleep(1)